1. Field of the Invention
The present invention relates to a non-contact type automatic multi-point diameter measurement apparatus capable of continuously measuring the diameter of a cylindrical work with high precision at a plurality of locations along the axis of the work in a real time manner.
2. Background of the Prior Art
Various devices are known for the measurement of diameters. For example, in the semiconductor manufacturing process, diameters of an as-grown single crystal ingot pulled up in a single crystal pulling apparatus were conventionally measured with calipers applied to different locations along the axis of the ingot.
In a single crystal pulling apparatus, the diameter of a single crystal ingot being pulled up is optically detected by means of an image sensor, and the accuracy of this image sensor is maintained by the adjustment thereof (such as zero point calibration in voltage) based on the actual diameter data (measured by the calipers) of the single crystal ingot which are supplied to the single crystal pulling apparatus in a feedback manner.
However, with the conventional manual measurement method, the result of the measurement is not free of the individual measurer's errors in determining the value, so that it is difficult to obtain reliable data with high precision. Furthermore, since the time efficiency of the measurement is not high due to the manual nature of the measurement, it is difficult to take diameters at a sufficient number of positions along the axis of the work (ingot), and, as a result, the data obtained are liable to be too insufficient to enable minute comparison between the actually measured values of the diameters (the diameters measured with calipers) and the diameter values detected by the image sensor of the single crystal pulling apparatus, so that an accurate determination of the errors in the latter values is difficult, and thus it is impossible to conduct a reliable adjustment of the accuracy of the image sensor, and, hence, it is impossible to attain high precision controlling of the diameter of the single crystal ingot grown in the single crystal pulling apparatus.